Conventionally, for example, in the optical technical field to which liquid crystal display devices and the like belong, there has been suggested to use a light diffusion film for which an incident light coming from a specific direction is diffused in specific directions while an incident light coming from other directions can be directly transmitted.
Different aspects of such a diffusion film are known but, in particular, a light diffusion film is widely known which includes, inside the film, a louver structure in which a plurality of plate-shaped regions with different refractive indices are alternately arranged along any one arbitrary direction along the film plane (for example, see Patent document 1).
Namely, Patent Document 1 discloses a method for producing a light control plate (light diffusion film) which includes a first step of retaining on a film a resin composition composed of a plurality of compounds, each having one or more polymerizable carbon-carbon double bonds in their molecules and having a refractive index that is different from the refractive indices of the other compounds, irradiating the composition with ultraviolet radiation from a specific direction and thereby curing the resin composition; and a second step of retaining the resin composition on the film of the cured product thus obtained, irradiating with ultraviolet radiation from a direction different from that of the first step, and thereby curing the resin composition, characterized in that the second step is repeated if necessary.
On the other hand, another type of light diffusion film is widely known which comprises, inside the film, a columnar structure composed of a plurality of pillars with comparatively high refractive index standing close together in regions with comparatively low refractive index (see, for example Patent Documents 2 and 3).
Namely, Patent Document 2 discloses a manufacturing device by which a light control plate (light diffusion film) is formed by opposing a linear light source to a photocurable resin composition film, and, while either the photocurable resin composition film or the linear light source, or both are being moved, by irradiating the photocurable resin composition film with light from the linear light source, thereby curing the composition. The device for manufacturing a light control plate (light diffusion film) is a device in which the axial direction of the linear light source crosses the moving direction, and in which a plurality of light blocking thin plates opposed to one another are provided between the photocurable resin and the linear light source at a predetermined interval in a direction almost perpendicular to the moving direction, in such a fashion that one edge facing the photocurable resin composition of each of the light blocking thin plates is parallel to the moving direction.
In addition, Patent Document 3 discloses a method for producing a light diffusion film in which a composition containing a photocurable compound is provided into a sheet, this sheet is irradiated with parallel radiations from a predetermined direction P, thereby curing the composition and forming aggregate bodies with multiple rod-shaped curable regions which are, inside the sheet, extended parallel to the P direction, the method being characterized in that, between the linear light source and the sheet, aggregates of tubular materials aligned parallel to the P direction are intercalated, and light is irradiated through the tubular materials.